1. Field of the Invention
The present invention relates to an electrical heating device with a frame which, on opposite sides, forms openings for the passage of a medium to be heated. The electrical heating device also has a layer structure arranged in the frame. In a direction transverse to the passage direction of the medium to be heated the said layer structure has several layers which are formed by corrugated-rib elements and at least one heat generating element. The heat generating element here comprises at least one PTC element arranged between parallel contact plates.
2. Description of the Related Art
An electrical heating device of this nature is for example known from DE 199 11 547, U.S. Pat. No. 5,854,471, EP 0 350 528 or DE 197 06 199.
The state of the art as presented in EP 2 161 514 A1 is also regarded as class-forming. This state of the art is also the basis of the problem definition which is also based on the present invention. This involves providing an electrical heating device of the generic type which enables an increased heating power with a compact construction.
Here, with generic electrical heating devices, due to the self-regulating properties of the PTC element there is the problem that with increasing temperature and also heating power the resistance of the PTC elements increases sharply so that the power dissipation of the PTC elements is reduced. Since, on the other hand, the electrical heating devices are particularly used in motor vehicles, they should have a compact design so that the suggestion that two electrical heating devices formed in the conventional way are arranged one behind the other in a HVAC in the flow direction or passage direction of the medium to be heated must be rejected, because it is contrary to the requirement of a compact design.
EP 2 161 514 A1 suggests that several corrugated-rib elements are arranged one behind the other in the direction of flow of the air to be heated and within a uniform frame. According to the prior-art suggestion at least two heating blocks are arranged one behind the other in the passage direction of the air to be heated. Here, the heating blocks are provided at least offset, i.e. the heat generating elements of the individual heating blocks are not directly situated one behind the other in the passage direction of the medium to be heated. Rather, they have a lateral spacing to one another in this passage direction in this otherwise parallel alignment of the layers of the various heating blocks relative to one another. The heat generating elements of one heating block are here located centrally behind the corrugated-rib elements of the other heating block. Here, the suggestion according to EP 2 161 514 A1 is obviously being led by the consideration that the exiting air heated in the flow direction of the front heating block has experienced the strongest heating directly adjacent to the heat generating element, whereas the central region in the extrapolated direction of the individual corrugated-rib elements experiences only a relatively slight heating of the air due to the largest distance of this central region from the heat generating element, so that this relatively cool air should meet according to the notion the region of strongest heating effect of the following heating block.
However, with the known suggestion, due to those heat generating elements, which are located after the through-flow corrugated-rib elements and arranged in their flow path, the passage openings for the air are displaced by the electrical heating device, whereupon a relatively high flow resistance results. Thus, however the heating power and the effectiveness of the electrical heating device is also reduced, because it is not solely defined by the temperature change caused by the electrical heating device, but rather by the amount of air heated by this temperature change. Furthermore, only part of the area provided for the heat exchange with the air is used, because the corrugated-rib elements located in the flow direction after the heat generating elements are shaded from these heat generating elements and namely by approximately one third of their area for a corrugated-rib height of 10 mm and a thickness of the heat generating element of approximately 3 mm.